tests: introduce write/read/verify test

Test misc-bdev-rw introduced.

The test writes buffers of various lengths to block device,
reads data back and verifies data read is the same as data written.

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>